This invention relates to drawing instruments, more particularly, to instruments having a lessened tendency to mar a drawing surface in use.
Drawing instruments such as triangles, T-squares and others are typically laid flat on a drawing surface with the entire area of the face of the instrument in contact with the surface. This leads to problems of smearing of pencilled or inked lines of a drawing, and of smearing or grinding debris from the drawing process, e.g., graphite and eraser residue, on or into the drawing surface, when the instrument slides thereacross. Also, ink tends to bleed under the edge of a flat-lying instrument used as a guide for scribing inked lines.
Previous attempts to alleviate the foregoing marring problems have included the provision of instrument-carried supports to space the instrument a slight distance from the drawing surface. The area of the supports in contact with the drawing surface is made substantially smaller than the face area of the instrument.
Fixed instrument supports, such as protuberances on the face of an instrument have been disclosed. However, the rubbing contact of even the small contact area of a protuberance with a drawing surface may cause marring.
Instrument supports are known which roll on the drawing surface, thus reducing rubbing friction thereon. These supports include rollable balls, and cylindrical rollers or wheels, revolving about an axis of rotation. The ball-type supports permit easy omni-directional relative movement over a drawing surface. The simple roller or wheel-type supports may be less advantageous, when they are easily rollable only in directions normal to the axis of rotation.
Prior drawing instruments having rolling members supporting an instrument body for movement over a drawing surface may be lacking, deficient, and/or disadvantageous in provisions for rendering the instrument immobile when used for drawing purposes, particularly while supporting the body in spaced apart relation to the drawing surface for avoidance of marring.